ALBIO5: THE OXGYEN DISASSOCIATION CURVE OF LARGE ORGANISMS IN RELATION TO SMALL ORGANISMS.

This unit dwells on the different gaseous components and elements in blood.

ox

The smaller the organisams the larger the surface area to volume ratio and the higher the metabolic, thus oxygen dissociation curve of the small organism would be to the right of the large ones because of haemoglobin must have a higher ability to unload the oxygen than to load it so as to provide it to the tissues that are metabolically using it at faster pane than in large ones.

DISSOCIATION CURVE OF MAN IN RELATION TO THE FLYING BIRD

E.g. pigeon.

Since a pigeon uses a lot of energy in flapping its wings while flying is oxygen dissociation curve will lie to the right of that blood (man)

sat

Effect of increased temperature on the position of haemoglobin dissociation curve.

Higher metabolism means more heat and hence raising the temperature and this occurs mainly in the tissues in the skeletal muscles during exercise.

  • A rise in blood temperature leans the affinity of haemoglobin for oxygen but increases its unloading and hence extra oxgyuen is released from the blood.
  • Thus increase in temperature shifts the dissociation curve to the right.

cav

  1. Ice fish which lives in Atlantic are the only vertebrates on the earth that lack haemoglobin.

They survive because at low water temperature, oxygen is much more soluble and their metabolic rate is also low and hence their oxygen demand is very low.

EFFECTS OF ALTITUDE

  • At high altitude, there is lower pressure and less oxygen in the atmosphere than at sea level. Mammals adapt to high altitude by increasing the number of red blood cells and the quantity of heamoglobin in their blood. Mammals which permanently at higher altitude posses variant haemoglobin which combines readily with oxygen.
  • These organisms that live at higher altitude have their dissociation curves to the left of those at lower altitude e.g. The Llama has its dissociation curve left to that of human because it lives at higher altitude where the pressure of the atmosphere makes it difficult to load haemoglobin with oxygen.
  • Therefore Llama haemoglobin must have a higher affinity to compensate for the above difficult.

ADAPTATIONS OF AQUATIC DIVING MAMMALS

E.g. seals.

Diving mammals posses adaptations which enable long submerged periods without breathing which include;

  1. Possession of large tidal volume.
  2. A high carrying oxygen capacity of the blood.
  • A low sensitivity of the respiratory centre to blood carbondioxide.
  1. A drop in heart rate and a redirection of blood to the brain at the expense of other parts of the body.

BOHR EFFECT

Effects of carbondioxide and oxygen dissociation curve

The Bohr Effect

  • Increase in carbondioxide tension of blood shifts the oxygen dissociation curve down wards and to the right and this is known as BOHR EFFECT or Bohr shift.
  • Therefore high carbondioxide tensions, the haemoglobin is less efficient at loading but more efficient at unloading it.
  • This is experienced in tissues where the release of oxygen is favoured because the carbondioxide is high due to its respiring cells.
  • In the lungs, the carbondioxide is lower due to its continued escape into atmosphere and this favours oxygen uptake.

EFFECTS OF PH ON OXYGEN DISSOCIATION CURVE

  • The lower the PH, the higher the acidity and hence the higher the CO2 content and hence the dissociation curve will shift downwards and to the right of that of the normal PH ( ~ 4).
  • The low PH is due to formation of carbonic acid from CO2 released from tissues dissolving in water.

OTHER BLOOD PIGMENTS

  • Many blood pigments differ in their prosthetic groups e.g. myoglobins, haemoglobin, chbrocruorins, haemocrythan contain iron while haemocuanin contains copper.
  • The blood pigments other than haemoglobin and myoglobin are confined to the lower animal e.g. worms, molluses and some cause one dissolved in plasma rather than within the cells.

EFFECTS OF CARBONDIOXIDE

  • Unfortunately haemoglobin combines more readily with carbonmonoxide, CO forming canbooy-haemoglobin.
  • This prevents 02 from taking up its position. H/W exercise 1, 2, 3 & 4, Pg 153-4 (J Simpkins).

BOHR EFFECT

This is increase in than loading of 02 from haemoglobin in areas with low 02 tensions and high C02 tension usually tissues.

TRANSPORT OF CARBONDIOXIDE

C02 is none soluble than 02 in water but its transport in solution is not adequate to meet the needs of most organisms. There are 3 methods of carrying C02 from the tissues to the respiratory surface.

  1. IN AQUEOUS

A small amount = 5% of C02 is transported in blood plasma sole.

IN COMBINATION WITH HAEMOGLOBIN

A little C02 around 10% combines with the amino groups in the fair polyptide chains which make up each haemoglobin module (Hb) to form carbaminohaemoglobin.

IN THE FORM OF HYDROGEN CARBONATE (HC03) ION

C02 diffuses into the RBC where it combines with H20 to form carbonic acid. The ……is catalyzed by the tine containing enzyme carbonic anhydrase.

Because of the presence of the enzyme in the RBC, most of the

C02  ~ 85% is coarried in it (cm form of HCO3).

 

– The carbonic acid then dissolates into hydrogen and HCO3 i.e.

                             Carbonic acid

H2O + C02                       H2CO3              H+ + HC03

 

  • If the H+ are left to accumulate, they raise the acidity of the RBC and may kill it. This is prevented by harmoglobin itself acting as a buffer (i.e. resisting changes in PH).
  • The presence of H+ encourages the oxyhaemoglobin to dissociate into haemoglobin and 02.
  • The 02 then diffuses out of the RBC to the tissues and the haemoglobin combines with the H+ ions forming a very weak acid i.e. haemoglobin HHb acid (HHb). Thus the Bohr effect is not actually due to C02 but the H+ ions.
  • The bicrbanate ions diffuse out of the RBC into the plasma where they combine with sodium ions (Na+) from the dissociation of Nacl to form sodium bicarbonate.

Na+ HCC3         NaHC03

  • The loss of negatively changed HCO3 ions from the RBC is balanced by the inward diffusion of negative chloride (Cl) ions from the dissociation the dissociation of NaCL. In this way, the electroneutradity of the RBC is restored.
  • A phenomenon known as the chloride shift.

Note:

When the RBC reaches the lungs the 02 tension is high all the reactions above into the reverse i.e. 02 is taken up by the RBC and C02 released.

 

ASSIGNMENT : THE OXGYEN DISASSOCIATION CURVE OF LARGE ORGANISMS IN RELATION TO SMALL ORGANISMS. MARKS : 100  DURATION : 2 days

 

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